Vascular diseases remain major causes of morbidity and mortality in the world. The availability of noninvasive imaging modalities for detection of features such as vessel wall inflammation and remodeling that are involved in, and increase the risk of vascular complications can help reduce this morbidity and mortality. Major existing gaps in the traditional approach to vascular imaging may be addressed by molecular imaging aimed at detecting relevant targets in vivo. To this means, tracers with broad specificity for matrix metalloproteinases (MMPs) have been developed and used to detect vascular remodeling and inflammation in vivo. While promising as first line agents, the effectiveness of these broadly specific agents is limited by diverse and at times opposing effects of different members of the MMP family in the pathogenesis of vascular remodeling and inflammation. Macrophage elastase (MMP-12) plays a key role in the development of atherosclerosis and aneurysm. RXP470, a selective and potent inhibitor of MMP-12, inhibits atherosclerotic plaque development and promotes a stable plaque phenotype. Here, we hypothesize that vessel wall inflammation and remodeling in atherosclerosis and aneurysm can be detected by molecular imaging of activated MMP-12 in vivo. Our specific aims are to develop and validate novel MMP-12-targeted tracers for molecular imaging and to validate the active form of MMP-12 as a marker of macrophage activation and target for imaging of vascular inflammation and remodeling in aneurysm and atherosclerosis. Based on the structure of RXP470 we have developed and preliminarily tested novel fluorescent and radiolabeled probes for molecular imaging. Here, this portfolio of tracers will be expanded and optimized for molecular imaging. The effectiveness of activated MMP-12 as a marker of inflammatory and vascular cell activation and differentiation will be addressed. Finally, complementary murine models of aneurysm and atherosclerosis will be used to validate MMP-12-targeted imaging for detection of vessel wall inflammation and remodeling by fluorescent imaging ex vivo and SPECT imaging in vivo. If validated, MMP-12 targeted imaging may identify patients at risk for acute coronary syndromes and aneurysm rupture and help track the effect of novel therapeutic interventions in vascular diseases.